JPH0883963A - Metal-based board - Google Patents

Abstract

PURPOSE: To improve the withstand-voltage characteristic of a metal-based board by a method wherein a metal foil is integrated with a metal plate via an insulating layer in which an inorganic filler within a specific range of volume % and a dispensing agent are contained. CONSTITUTION: An inorganic filler, in 65 to 89vol.%, which is insulating and whose thermal conductivity is good and a dispensing agent are filled into an insulating layer 2 constituting a resin component such as an epoxy resin, a phenol resin or the like. Via the insulating layer 2, a metal foil 1 which is conductive such as a copper foil, an aluminum foil or the like is integrated with a metal plate 3 such as an aluminum plate, an iron plate or the like. Thereby, even when the insulating layer 2 contains the inorganic filler in large quantities, it is possible to realize a metal-based board which can restrain a microvoid from being generated and which is excellent in a withstand-voltage characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal base board for printed wiring boards.

[0002]

2. Description of the Related Art Power transistors and hybrid ICs
Good heat dissipation is required for a substrate for high-density mounting of components that generate a large amount of heat as described above. The metal base substrate is a substrate in which the insulating layer 2 is formed on one surface of the metal plate 3 and the metal foil layer 1 is provided on the insulating layer 2 (see FIG. 1), and has good heat dissipation.

In order to further improve the heat dissipation of a metal base substrate which is said to have good heat dissipation, there is known a metal base substrate in which an insulating layer contains an inorganic filler, particularly a high thermal conductive filler such as alumina.

[0004]

However, when a large amount of the inorganic filler is contained, there is a problem that dielectric breakdown between the conductor layer and the metal plate is likely to occur and the withstand voltage characteristic is deteriorated. It is an object of the present invention to improve withstand voltage characteristics of a metal base substrate, particularly a metal base substrate having an insulating layer containing a large amount of inorganic filler.

[0005]

MEANS FOR SOLVING THE PROBLEMS The present inventors have found that a metal base substrate having an insulating layer highly filled with an inorganic filler is liable to have microvoids and is liable to cause a dielectric breakdown due to an interface between the inorganic filler and a resin. The inventors have found that the voltage characteristics are inferior and have reached the present invention.

According to the present invention, in a metal base substrate comprising a metal foil, an insulating layer and a metal plate, the insulating layer contains an inorganic filler having high thermal conductivity and a dispersant for modifying the surface of the inorganic filler. And

The metal foil 1 is not particularly limited as long as it has conductivity such as copper foil and aluminum foil.

The metal plate 3 is an aluminum plate, an iron plate, or the like.
As long as it is used for a metal base substrate,
There is no particular limitation.

As the resin component constituting the insulating layer 2, epoxy resin, phenol resin, bismaleimide resin, phenoxy resin, a mixed resin thereof or the like can be used.

The resin constituting the insulating layer 2 is filled with an inorganic filler having an insulating property and good thermal conductivity in an amount of 65 to 80% by volume, preferably 70 to 80% by volume. Examples of the inorganic filler used here include powders of oxides such as alumina, magnesium oxide and beryllium oxide having a volume resistivity of 10 ¹⁰ Ω · cm or more and a thermal conductivity of 20 W / cm · s · ° C or more, aluminum nitride, nitriding. A powder of nitride such as boron or a powder of diamond can be used. Further, when the inorganic filler having a single particle size is filled at 65% by volume or more, voids are inevitable. Therefore, it is necessary to use an inorganic filler having a wide particle size distribution, but the present invention is not limited to this.

As the dispersant used in the present invention, a copolymer having a functional group such as a carboxyl group, a nitrile group, an acrylamide group, an aminoamide group, a pyridyl group, a hydroxyl group, a hydroxyester group and an ethylene oxide group in the molecule. -Based dispersants, nonionic dispersants of ester type, ether type, ester ether type, nitrogen-containing type, etc., aliphatic amine salts, aromatic amine salts, heterocyclic amine salts, alkyl amines, polyalkylene polyamine derivatives, etc. Dispersants of In addition, the composition of the dispersant is not limited as long as the dispersant is effective to modify the surface of the inorganic filler and disperse it in the resin, and it can be used in combination with a leveling agent or an antifoaming agent.

When alumina is used as the inorganic filler, a copolymer-based dispersant having a functional group is particularly effective. Examples of such a dispersant include, for example, ICI in England.
A copolymer-based dispersant having a carboxyl group, an ethylene oxide group, and a hydroxy ester group is commercially available from the same company. Also, a copolymer-based dispersant having a hydroxyl group, an aminoamide group, a carboxyl group, and an ethylene oxide group is commercially available from Bick Chemie GmbH, Germany.

The thermosetting resin varnish containing a large amount of inorganic filler can be produced by a raking machine, a kneader, a ball mill, a roll mill, etc., alone or in combination. The kneading method is not particularly limited as long as the inorganic filler can be sufficiently dispersed. Further, it is desirable to remove air bubbles in the varnish by vacuum degassing or ultrasonic degassing after the varnish is produced.

[0014]

According to the present invention, the surface of a large amount of the inorganic filler contained in the insulating layer can be modified by adding a dispersant to the varnish which forms the insulating layer. This facilitates the deaeration of the bubbles in the varnish and reduces the microvoids. Further, it also has an effect of suppressing the sedimentation of the inorganic filler, and an insulating layer in which the inorganic filler is uniformly dispersed can be obtained.

[0015]

【Example】

Preparation of Varnish 1 30 parts by weight of solid epoxy resin (using Epicoat 1001 manufactured by Yuka Shell Epoxy Co., Ltd.), 50 parts by weight of liquid epoxy resin (using Epicoat 828 manufactured by Yuka Shell Epoxy Co., Ltd.) Part, phenoxy resin (using Toyo Kasei Co., Ltd., trade name YP-50) 20
35 parts by weight of fail novolak resin (using HP850N, trade name of Hitachi Chemical Co., Ltd.), 0.5 parts of cyanoethylated-2-phenylimidazole (using 2PZ-CN, trade name of Shikoku Chemical Co., Ltd.) 0.5 Parts by weight,
γ-glycidoxy-propyltrimethoxysilane (silane coupling agent: product name NU of Nippon Unicar Co., Ltd.
C. A-187) 3.3 parts by weight, alumina filler (particle size 1 to 40 .mu.m, average particle size 10 .mu.m, Showa Denko KK trade name AS-50 used) 450 parts by weight with a ball mill, sufficient filler. Mixed until dispersed.

Preparation of varnish 2 With the composition of varnish 1, the compounding amount of alumina filler was 102
The content was changed to 0 part by weight, and mixed by a ball mill until the filler was sufficiently dispersed.

Preparation of Varnish 3 In the composition of Varnish 2, a dispersant containing an alkyl (2-4) phenol / phenylphenol / formaldehyde condensate as a component (Big Chemie Japan Co., Ltd., trade name D
10 parts by weight of isperbyk-110) were mixed and mixed in a ball mill until the filler was sufficiently dispersed.

Preparation of Varnish 4 From the composition of Varnish 3, the silane coupling agent was changed to 7 parts by weight, and the dispersant was composed of a polymerized fatty acid / polyethylene polyamine / fatty acid polycondensate and a styrene oxide adduct as a component ( Big Chemie Japan Co., Ltd., trade name Disperbyk-161) was changed to 20 parts by weight, and mixed by a ball mill until the filler was sufficiently dispersed.

Preparation of Varnish 5 From the composition of Varnish 3, the silane coupling agent was changed to 7 parts by weight, the compounding amount of the dispersant was changed to 13 parts by weight, and further,
Alumina filler, 900 parts by weight of the AS-50,
Similarly, the trade name AL-45-1 of Showa Denko KK is 40
The content was changed to 0 part by weight, and mixed by a ball mill until the filler was sufficiently dispersed.

Example 1 A copper foil (Furukawa Electric Co., Ltd., trade name GTS-70) having a thickness of 70 μm was coated with the varnish 3 and dried by heating to form an insulating layer in a B stage state having a thickness of 100 μm. Formed. The above-mentioned copper foil with an insulating layer and an aluminum plate having a thickness of 1.5 mm were superposed and heated and pressed at 170 ° C. for 90 minutes under a pressing condition of 40 MPa to obtain a metal base substrate. The filling rate of the inorganic filler was 70% by volume.

Example 2 A metal base substrate was obtained in the same manner as in Example 1 except that the varnish 4 was used. The filling rate of the inorganic filler was 70% by volume.

Example 3 A metal base substrate was obtained in the same manner as in Example 1 except that the varnish 5 was used. The filling rate of the inorganic filler was 75% by volume.

Example 4 A copper foil (Furukawa Electric Co., Ltd., trade name GTS-70) having a thickness of 70 μm was coated with the varnish 3 and dried by heating to form an insulating layer in a B stage state having a thickness of 100 μm. Formed. 120mm aluminum plate with a thickness of 1.5mm for 5 minutes
It is heated to ℃, on top of which the copper foil with insulating layer is placed at 160 ℃
After heating and pressurizing with a laminator under the condition of linear pressure of 196 N / cm, it was heated and cured at 170 ° C. for 60 minutes to obtain a metal base substrate. The filling rate of the inorganic filler was 70% by volume.

Comparative Example 1 A metal base substrate was obtained in the same manner as in Example 1 except that Varnish 1 was used. The filling rate of the inorganic filler was 50% by volume.

Comparative Example 2 A metal base substrate was obtained in the same manner as in Example 1 except that the varnish 2 was used. The filling rate of the inorganic filler was 70% by volume.

Table 1 shows the thermal resistance (unit: ° C / W) and withstand voltage (unit: kV) of the metal base substrate obtained above.
From these results, it can be seen that the metal base substrates of the examples of the present invention have low thermal resistance and excellent withstand voltage characteristics.

[0027]

[Table 1]

The methods for measuring thermal resistance and withstand voltage are as follows. Thermal resistance: Place a test piece on a heat dissipation block made of aluminum metal, apply a DC voltage to the transistor soldered on the copper foil of the test piece, measure the temperature of the transistor and heat dissipation block, and measure the temperature of both. It is calculated by dividing the difference by the applied power. Withstand voltage: The voltage at which the insulating material is not destroyed when continuously boosted at a boosting rate of 500 V / sec.

[0029]

As described above, according to the present invention, it is possible to suppress the generation of microvoids even when the insulating layer contains a large amount of inorganic filler, and to provide a metal base substrate having excellent withstand voltage characteristics. It becomes possible.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a metal base substrate of the present invention.

[Explanation of symbols]

 1 Metal foil 2 Insulation layer 3 Metal plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiromi Senba, 1500, Ogawa, Ogawa, Shimodate-shi, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Shimodate Laboratory

Claims (2)

[Claims] 1. A metal base substrate in which a metal foil is integrated with a metal plate through an insulating layer containing 65 to 80% by volume of an inorganic filler and a dispersant. 2. The metal-based substrate according to claim 1, wherein the dispersant is a copolymer having a functional group having a strong affinity for an inorganic substance in the molecule.